Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$71.51	9.157%	$78.0582	$78.06	$78.05	$78.10
Purchase #2	$191.83	5.750%	$202.8602	$202.86	$202.85	$202.90
Purchase #3	$242.37	11.235%	$269.6003	$269.60	$269.60	$269.60
Purchase #4	$70.93	5.734%	$74.9971	$75.00	$75.00	$75.00
Purchase #5	$73.52	13.714%	$83.6025	$83.60	$83.60	$83.60
Purchase #6	$73.36	6.386%	$78.0448	$78.04	$78.05	$78.00
Purchase #7	$117.79	11.707%	$131.5797	$131.58	$131.60	$131.60
7 purchase totals =	$841.31		$918.7428	$918.74	$918.75	$918.80